Insert chip of oil-drilling tricone bit, manufacturing method thereof and oil-drilling tricone bit

Abstract

An insert chip of an oil-drilling tricone bit includes an insert-chip substrate made of a cemented carbide of a first composition, and further includes a cemented carbide coating layer constituted of at least two stacked coating layers made of a cemented carbide of a composition different from the first composition. The cemented carbide coating layer covers the whole of a cutting edge of the insert-chip substrate. The coating layers each have a thickness, at a tip portion of the cutting edge, in a range from 0.1 mm to 2.5 mm, and the total thickness of the cemented carbide coating layer is in a range from 1 mm to 5 mm. The coating layers include an outermost cemented carbide layer and at least one intermediate coating layer in addition to the outermost cemented carbide layer, and the outermost cemented carbide layer has a hardness higher than that of the at least one intermediate coating layer and of the insert-chip substrate.

What is claimed is:  
     
       1. An insert chip of an oil-drilling tricone bit comprising: 
       a substrate that is made of a first cemented carbide of a first composition and that includes a cylindrical body and a cutting edge for drilling; and  
       a plurality of coating layers successively stacked on said substrate and covering at least 80% of a total surface area of said cutting edge of said substrate;  
       wherein:  
       said plurality of coating layers includes an outermost coating layer that comprises a second cemented carbide of a second composition different from said first composition, that is located directly at and forms an exposed outermost surface of said insert chip, and that has a thickness in a range from 0.1 mm to 2.5 mm at a tip portion of said cutting edge;  
       said plurality of coating layers further comprises an intermediate coating layer that comprises a third cemented carbide of a third composition different from said first composition, that is disposed between said substrate and said outermost coating layer, and that has a thickness in a range from 0.1 mm to 2.5 mm at said tip portion of said cutting edge;  
       said plurality of coating layers has a total thickness in a range from 1 mm to 5 mm; and  
       said outermost coating layer has a hardness greater than a hardness of said intermediate coating layer and greater than a hardness of said substrate.  
     
     
       2. The insert chip of an oil-drilling tricone bit according to  claim 1 , wherein said plurality of coating layers covers 100% of said total surface area of said cutting edge. 
     
     
       3. The insert chip of an oil-drilling tricone bit according to  claim 1 , wherein said intermediate coating layer is an anti-chipping layer, of which said third composition contains Co with a higher Co content than said second composition of said outermost coating layer, or contains WC particles with a larger WC particle size than said second composition of said outermost coating layer. 
     
     
       4. The insert chip of an oil-drilling tricone bit according to  claim 1 , wherein said intermediate coating layer is an anti-chipping layer of which said third composition contains Co with a higher Co content than said first composition of said substrate. 
     
     
       5. The insert chip of an oil-drilling tricone bit according to  claim 4 , wherein said anti-chipping layer contains Co particles including special Co particles each elongated in a radial direction of said insert chip in a vertical cross-sectional structure of said insert chip and each having a ratio of a length in the radial direction of said insert chip relative to a length in an axial direction of said insert chip being in a range from 3 to 100, and said special Co particles constitute at least 5% by volume of all of said Co particles contained in said anti-chipping layer. 
     
     
       6. The insert chip of an oil-drilling tricone bit according to  claim 1 , wherein said outermost coating layer contains WC particles having an average particle size of at most 1 μm. 
     
     
       7. The insert chip of an oil-drilling tricone bit according to  claim 1 , wherein said outermost coating layer has a compressive residual stress. 
     
     
       8. The insert chip of an oil-drilling tricone bit according to  claim 7 , wherein said compressive residual stress is in a range from 0.05 GPa to 0.80 GPa. 
     
     
       9. The insert chip of an oil-drilling tricone bit according to  claim 1 , wherein only said outermost coating layer among said plurality of coating layers further contains diamond particles embedded in said second cemented carbide, and said diamond particles have a particle size in a range from 10 μm to 100 μm and constitute 5% to 40% by volume of said outermost coating layer. 
     
     
       10. The insert chip of an oil-drilling tricone bit according to  claim 9 , further comprising at least one of a refractory metal and a ceramic covering each of said diamond particles as a covering layer of at most 1 μm in thickness. 
     
     
       11. The insert chip of an oil-drilling tricone bit according to  claim 1 , wherein said outermost coating layer has a micro Vickers hardness of at least 15 GPa. 
     
     
       12. An oil-drilling tricone bit having as its cutting edge the insert chip of an oil-drilling tricone bit according to  claim 1 . 
     
     
       13. The insert chip of an oil-drilling tricone bit according to  claim 1 , wherein said plurality of coating layers further includes another coating layer that comprises a fourth cemented carbide of a fourth composition different from said first composition, that is disposed between said substrate and said outermost coating layer, and that has a thickness in a range from 0.1 mm to 2.5 mm at said tip portion of said cutting edge. 
     
     
       14. The insert chip of an oil-drilling tricone bit according to  claim 1 , wherein said plurality of coating layers does not contain any diamond particles. 
     
     
       15. The insert chip of an oil-drilling tricone bit according to  claim 1 , wherein said second cemented carbide of said outermost coating layer comprises particles of a carbide bonded together by a bonding metal. 
     
     
       16. The insert chip of an oil-drilling tricone bit according to  claim 15 , wherein said carbide is tungsten carbide (WC) and said bonding metal is cobalt (Co). 
     
     
       17. The insert chip of an oil-drilling tricone bit according to  claim 15 , wherein said outermost coating layer consists of said particles of said carbide and said bonding metal. 
     
     
       18. A method of manufacturing the insert chip of an oil-drilling tricone bit according to  claim 1 , comprising the following steps: 
       an inserting step of inserting said substrate into a die;  
       a stacking step of stacking, on said substrate, cemented carbide powders to form said plurality of coating layers having said total thickness after being sintered; and  
       a sintering step of performing electrical pressure sintering, by using a punch inserted into said die, said punch having a depressed end which matches in shape a desired finished protruded cutting edge of said insert chip, applying a pressure in a range from 20 MPa to 50 MPa, and controlling the temperature of said punch within a temperature range from 1500° C. to 1800° C.  
     
     
       19. The method of manufacturing an insert chip of an oil-drilling tricone bit according to  claim 18 , wherein in said sintering step, said sintering is performed for a period in a range from 5 minutes to 20 minutes. 
     
     
       20. An insert chip of an oil-drilling tricone bit comprising: 
       an insert-chip substrate made of a cemented carbide of a first composition, said substrate including a cylindrical body and a cutting edge for drilling; and  
       a cemented carbide coating layer formed of at least two stacked coating layers made of a cemented carbide of a composition different from said first composition, said cemented carbide coating layer covering at least 80% of a surface area of said cutting edge of said insert-chip substrate; wherein  
       said coating layers each have a thickness, at a tip portion of said cutting edge, in a range from 0.1 mm to 2.5 mm, and the total thickness of said cemented carbide coating layer is in a range from 1 mm to 5 mm,  
       said coating layers include an outermost cemented carbide layer and at least one coating layer besides said outermost cemented carbide layer, and said outermost cemented carbide layer has a hardness higher than that of said at least one coating layer and of said insert-chip substrate, and  
       said outermost cemented carbide layer contains WC particles of an average particle size of at most 1 μm.  
     
     
       21. An insert chip of an oil-drilling tricone bit comprising: 
       an insert-chip substrate made of a cemented carbide of a first composition, said substrate including a cylindrical body and a cutting edge for drilling; and  
       a cemented carbide coating layer formed of at least two stacked coating layers made of a cemented carbide of a composition different from said first composition, said cemented carbide coating layer covering at least 80% of a surface area of said cutting edge of said insert-chip substrate; wherein  
       said coating layers each have a thickness, at a tip portion of said cutting edge, in a range from 0.1 mm to 2.5 mm, and the total thickness of said cemented carbide coating layer is in a range from 1 mm to 5 mm,  
       said coating layers include an outermost cemented carbide layer and at least one coating layer besides said outermost cemented carbide layer, and said outermost cemented carbide layer has a hardness higher than that of said at least one coating layer and of said insert-chip substrate, and  
       only said outermost cemented carbide layer among said coating layers contains diamond particles of a particle size in a range from 10 μm to 100 μm and said diamond particles constitute 5% to 40% by volume of said outermost cemented carbide layer.  
     
     
       22. An insert chip of an oil-drilling tricone bit comprising: 
       an insert-chip substrate made of a cemented carbide of a first composition, said substrate including a cylindrical body and a cutting edge for drilling; and  
       a cemented carbide coating layer formed of at least two stacked coating layers made of a cemented carbide of a composition different from said first composition, said cemented carbide coating layer covering at least 80% of a surface area of said cutting edge of said insert-chip substrate; wherein  
       said coating layers each have a thickness, at a tip portion of said cutting edge, in a range from 0.1 mm to 2.5 mm, and the total thickness of said cemented carbide coating layer is in a range from 1 mm to 5 mm,  
       said coating layers include an outermost cemented carbide layer and at least one coating layer besides said outermost cemented carbide layer, and said outermost cemented carbide layer has a hardness higher than that of said at least one coating layer and of said insert-chip substrate, and  
       said outermost cemented carbide layer has a micro Vickers hardness of at least 15 GPa.